At this moment there is the opinion that
gradient elasticity models with the negative sign in
equations (REF )
cannot be obtained from lattice models [1]}.
It is usually assumed that this class of the second-gradient models does not
have a direct relationship with discrete microstructure and
lattice models [2]}.
It was proved that the homogenization (continualization) procedure,
which is considered in [3]}, [4]}, [5]}, [6]}, [7]},
uniquely leads to a second-order
strain gradient term that is preceded by a positive sign.
The second-gradient model with negative sign
cannot be derived by this homogenization procedure.
From a mathematical point of view it is caused by properties
of the Taylor series that is used in this procedure.
